The landing of Apollo 11 on the Moon on July 20, 1969, when Neil Armstrong and Buzz Aldrin walked on the lunar surface while Michael Collins orbited above — watched or heard by perhaps a fifth of humanity, the climax of the Cold War space race, the farthest people have ever traveled, and a frontier the species reached and then stepped back from for half a century.
On 20 July 1969, two human beings stood on a world that was not the Earth. Neil Armstrong climbed down a ladder onto gray dust no living thing had ever touched, and roughly six hundred million people watched or listened as it happened. It was the farthest anyone had ever gone, and it remains so. Twelve Americans walked the Moon between 1969 and 1972. Then the visits stopped. No one has returned since. The most ambitious journey our species ever made was also, for fifty years, its last step outward.